Transportable refrigeration system

ABSTRACT

TO BE CONNECTED WITH THE OUTER TUBE AT THE OTHER END OF THE TUBE ARRAY. AN EXTENSION ON THE INNER TUBE OF THE OTHER END OF THE ARRAY LEADS TO THE UPPER PORTION OF THE CONDENSER-ACCUMULATOR FOR PASSING THE REFRIGERANT VAPOR OVER THE CONDENSING SURFACES, AND THE CONDENSED REFRIGERANT COLLECTED AT THE BOTTOM IS FED INTO THE ANNULAR SPACE OF THE ARRAY FOR RECIRCULATION. A DRIVEN TWO-CYLINDER CRYOGENIC ENGINE OPERATING ON A MODIFIED STIRLING CYCLE AND USING A FIXED GAS AS THE WORKING FLUID AND DISPOSED OUTSIDE THE AREA TO BE COOLED AND HAVING A COLD HEAD IN THERMAL CONNECTION WITH THE CONDENSER-ACCUMULATOR, SERVES AS THE COOLING MEANS FOR THE REFRIGERANT VAPOR.   A TRANSPORTABLE REFRIGERATION SYSTEM FOR COOLING AN ENCLOSED AREA COMPRISES A TRANSPORTATABLE VEHICLE HAVING AN ENCLOSED AREA TO BE COOLED, AND A TUBE ARRAY DISPOSED IN THE AREA SERVES AS THE COOLER. ITS CONSISTS OF TWO SPACED CONCENTRIC TUBES WITH THE OUTER TUBE CLOSED ON ONE END. THIS ARRAY SERVES TO FEED LIQUID REFRIGERANT (B.PT. 50* C. TO-50* C.), MAINLY BY CAPILLARY ACTION, THROUGH THE ANNULAR SPACE BETWEEN THE TUBES, WHEREIN EVAPORATION OF THE REFRIGERANT EFFECTS A COOLING ACTION AND THE SPACE WITHIN THE INNER TUBE SERVES TO COLLECT SEPARATED VAPOR EMITTED BY THE REFRIGERANT DURING THE COOLING OPERATION. AN ENCLOSED CONDENSER-ACCUMULATOR CONTAINING A MULTIPLICITY OF CONDENSING SURFACES AND HAVING A THERMAL CONNECTION SERVES AS THE CONDENSER AND RECEPTACLE FOR THE REFRIGERANT. IT HAS AN OPENING NEAR ITS BOTTOM DESIGNED

March 6, 1973 s. F. MALAKER 3,719,051

'IHANSPORTABLE REFRIGERATION SYSTEM Filed Oct. 26. 1971 5 Sheets-Sheet 1 IN VENTOR,

STE PHEN F. MALAKER ATTORNEY March 6, 1973 s. F. MALAKER TRANSPORTABLE REFRIGERATION SYSTEM 5 Sheets-Sheet 2 Filed Oct. 26. 1971 FIG. 2

a n1 a 5 m w V/// M mm 7 2 2 a I 3 3 m 3 F a M. 2 H 3 5 WW u may. m

STEPHEN F. MALAKER ATTORNEY March 6, 1973 s. F. MALAKER TRANSPORTABLE REFRIGERATION SYSTEM 5 Sheets-Sheet 5 Filed Oct. 26. 1971 FIG. 4

FIG.

INVENTOK S TE PHEN F. MALAKER A T TOR/VEV March 6, 1973 s. F. MALAKER 3,719,051

TRANSPORTABLE REFRIGERATION SYSTEM Filed Oct. 26. 1971 5 Sheets-Sheet 4.

ll 1 l? INVENTOR. STEPHEN F. MALAKER ATTORNEY S- F. MALAKER TRANSPORTABLE REFRIGERATION SYSTEM 5 Sheets-Sheet 5 FIG.

I N VEA' TOR. STEPHEN F. MALAKER BY 03,

ATTORMY March 6, 1973 Filed Oct. 26, 1971 United States Patent O M 3,719,051 TRAN SPORTABLE REFRIGERATION SYSTEM Stephen F. Malaker, Mountainside, N.J., assignor to Romayne Corporation, Mountainside, NJ. Continuation-impart of application Ser. No. 8,537, Feb. 4, 1970. This application Oct. 26, 1971, Ser. No. 192,128 Int. Cl. F25p 9/00; F2511 17/00 U.S. Cl. 626 9 Claims ABSTRACT OF THE DISCLOSURE A transportable refrigeration system for cooling an enclosed area comprises a transportable vehicle having an enclosed area to be cooled, and a tube array disposed in the area serves as the cooler. It consists of two spaced concentric tubes with the outer tube closed on one end. This array serves to feed liquid refrigerant (B.Pt. 50 C. to 50 C.), mainly by capillary action, through the annular space between the tubes, wherein evaporation of the refrigerant effects a cooling action and the space within the inner tube serves to collect separated vapor emitted by the refrigerant during the cooling operation. An enclosed condenser-accumulator containing a multiplicity of condensing surfaces and having a thermal connection serves as the condenser and receptacle for the refrigerant. It has an opening near its bottom designed to be connected with the outer tube at the other end of the tube array. An extension on the inner tube of the other end of the array leads to the upper portion of the condenser-accumulator for passing the refrigerant vapor over the condensing surfaces, and the condensed refrigerant collected at the bottom is fed into the annular space of the array for recirculation. A driven two-cylinder cryogenic engine operating on a modified Stirling cycle and using a fixed gas as the Working fluid and disposed outside the area to be cooled and having a cold head in thermal connection with the condenser-accumulator, serves as the cooling means for the refrigerant vapor.

CROSS REFERENCES TO RELATED APPLICATION This application is a continuation-in-part of copending application Ser. No. 8,537, filed on Feb. 4, 1970, now abandoned, by Stephen F. Malaker.

BACKGROUND OF THE INVENTION This invention relates to a transportable refrigeration system which is adapted for the cooling of enclosed areas in trucks, trailers, buses, trains, and other vehicles.

A search of the prior art has disclosed U.S. Pat. No. 2,889,686 which depicts a displacer-type cold gas engine designed to cool and recycle liquid nitrogen which is used for cooling a space. This type of nitrogen liquefier engine has been found to not only have an excessive weight, but it also has been found to exhibit a low etficiency in the temperature range desired for commercial refrigeration of food trucks, for example. Also, the single cooling coil system depicted is prone to develop a gas pocket in the coil.

In U.S. Pats. 2,350,348 and 2,448,261, a household refrigerator is described wherein the lower temperature space is cooled with a conventional motor-compressor unit employing expansion coils, some of which are used to cool the liquid reservoirs of a number of sealed vertical tubes extending into the higher temperature space of the refrigerator. The vertical tubes are nearly completely filled with sintered metal or bundles of glass fibers, and the liquid portions are filled with ammonia or other volatile liquid. As far as the present invention ICE is concerned, such a system would be impractical for the purpose because it would not accomplish much more than the present motor-compressor units now used in trucks. Furthermore, since truck-trailers of 40 ft. lengths are not uncommon, sintered metal rods or glass fiber bundles would induce excessive hydrodynamic frictional losses during liquid transfer, resulting in too slow a cooling rate. 7

Although heat pipes of the type of that shown in U.S. Pat. No. 3,528,494 have been described for heating purposes, there has been no suggestion, as far as known, of the use of a modified Stirling engine in combination with the present tube array for commercial cooling of vehicles as outlined in the present invention.

U.S. Pat. No. 3,468,300 describes a railway tank car which is heated or cooled by means of a heat pipe. However, the cooling is effected by a conventional refrigeration cycle employing a compressor, condenser, expansion valve, etc. The volatile liquid refrigerant is employed to cool the outside of the heat pipe, while the inner working fluid is ethylene glycol. On the other hand, the volatile refrigerant of the present invention is employed within the tube array in a much less complicated and more efficient system.

SUMMARY OF THE INVENTION According to the present invention, a light weight refrigeration system is provided having a high efiiciency and capable of much better performance than the units now in use. Briefly, it consists of (1) a transportable vehicle, (2) a tube array disposed within an enclosed space to be cooled in said vehicle and comprising a pair of concentric tubes, the outer tube being closed on one end, (3) a liquid refrigerant boiling between 50 C. to 50 C. which is fed, mainly by capillary action, within the annular space between the two tubes, (4) an enclosed condenser-accumulator containing a multiplicity of condensing surfaces and having a thermal connection and connectable to the tube array in a manner such that the condensed refrigerant may be fed into the annular tube space while vapor issuing from within the inner tube is led to the upper portion of the condenser-accumulator for liquefaction, (5) a driven 2-cylinder modified Stirling cycle cryogenic engine operating on a fixed gas and disposed on the outside of the area to be cooled and having a cold head in thermal connection with the condenser-accumulator, and (6) driving means on the vehicle for driving the engine.

The transfer of refrigeration from the closed cycle cryogenic engine to the load is accomplished mainly by flow of liquid refrigerant of the tube array, and is closely dependent upon the physical characteristics of the refrigerant. This liquid transport factor (L.T.F.) may be defined (in units of B.t.u./hr. ft. for example, as:

where Hv is the latent heat of vaporization, o is the surface tension, and 7 is the kinematic viscosity of the liquid refrigerant at operating temperatures. This L.T.F. has the dimensions of thermal flux.

From the foregoing, it is apparent that the refrigerative capacity of the tube array of the present invention is dependent upon the latent heat, the surface tension, and the viscosity of the refrigerating liquid medium. In the tube array of the present invention, it is necessary to provide for egress of vapor liberated at very high velocity between the tubes. In the case of short tubes, the vapor can travel to the end of the annular array space and then pass into the central portion thereof for transfer to the liquefaction portion of the system. In the case of longer tubes,

it has been found necessary to provide perforations or openings along the inner tube to permit vapor to pass through the wall thereof and enter the central Withdrawal area of the array. This foraminous nature of the inner tube does not interfere with the capillary flow of liquid along the wall. A uniform perforation or porosity permits efficient liquid-vapor separation and enables the liquid phase to remain in intimate contact with the external heat transfer wall of the outer tube where it is most effective, while eliminating the inherent deficiencies of 2-phase flow in the annulus.

By controlling the temperature of the cryogenic engine output, the tube array can be subcooled so that sensible heat of the liquid can also be utilized, in addition to the heat of vaporization. Thus, for load matching or heat balance purposes, the operating point of a given refrigerant liquid in the array can be varied in accordance with the temperature-pressure curves. This additional flexibility of operation is not available in conventional refrigeration systems wherein liquid refrigerant in the evaporator, whch is the sole source of refrigeration, is a part of the flow process from compressor through condenser through evaporator.

A cryogenic engine, as defined herein, is a closed-cycle unit operating on a gas which is not liquefied under the operating conditions (i.e., a fixed gas). Such a gas is helium or other fixed gas operating in the non-condensing temperature range. The engine must be one operating on a modified Stirling cycle. The Stirling cycle, which was an ideal cycle, was based upon piston motions which would allow the four steps of the cycle (i.e., the isothermal compression, the constant-volume gas transfer from compression space to expansion space, the isothermal expansion, and the constant-volume gas transfer from expansion space to compression space) to be made independently, consecutively and cyclically. However, the pistons of commercial cryogenic engines driven by a crankshaft move approximately harmonically and, consequently, the cycle is not ideal and, for this reason, it is called a modified Stirling cycle.

Modified Stirling cycle engines may be classified broadly as follows: (1) The 2-cylinder engines (wherein the working space is divided between two separate cylinders, one of which forms the hot space, and the other the cold space, with the regenerator disposed between), and (2) the displacer-type engines (using one cylinder, with volume variations of the hot space controlled by the movement of a displacer). There is a third type wherein a piston and displacer are housed in separate cylinders, but this type is not a very practical one.

A modified Stirling cycle engine, adaptable for the present invention, must be capable of eificiently developing a cold head temperature of at least -40 C. and, desirably, at least 60" C., or below, at the thermal connection. The latter is desirably an abuttable surface of copper, silver, aluminum, or other highly conductive material which is abutted against another thermal connection, such as that of the condenser-accumulator of the present invention. A highly efiicient cryogenic engine found to be adequately suited for the industrial temperature range and purposes of the present invention is a 2-cylinder modified Stirling cycle engine marketed under the trademark Cryomite, and made in accordance with the Malaker et al. US. Pat. No. 3,074,244. Such an engine, besides being highly efficient in the desired temperature range, is light in weight and is admirably suited for transport uses. It is operable by an electric motor which may be connected to the battery of the vehicle, or to a separately-driven generator carried by the vehicle.

In simplified terms, the system of the present invention operates as follows: Using the tube array as a heat sink for the load, and a heat source for the refrigerator, heat is removed from the liquefiable refrigerating liquid, and the vapor therefrom is subject to contact with a multiplicity of condensing surfaces which are cooled through the thermal connection with the cold head of the cryogenic engine. The vapor is liquefied rapidly and recycled in the annulus between the tubes of the array. The liquid refrigerant travels the length of the annular space by means of capillary action due to the surface tension forces of the liquid, augmented by Bernouilli and gravity forces. As the liquid travels through the annulus, a portion of it is vaporized and the vapors pass into the center space of the array through which it travels at a very high velocity for liquefaction at the condensing surfaces in the condenser-accumulator.

The volatile liquefiable refrigerant suitable for use in the tube array of the present invention must be a readilyliquefiable low boiling compound having a boiling point at one atmosphere within the range of about 50 C. to about 50 C. Suitable compounds for this purpose include fiuoro-chloro hydrocarbons, such as those sold under the trademark Freon and exemplified by dichlorodifluoro methane (B.Pt. 28 C.), as well as methyl chloride (B.Pt. 24.4 C.), butane (B.Pt. -6 C.), propane (B.Pt. 42 C.), butylamine (B.Pt. 16.6 C.), and the like. The transportable vehicle, which is a part of the present invention, may be a truck, trailer, tractortrailer freight car, tank car, airplane, ship, or the like. Such a vehicle requires a light weight cooling system having a high efficiency in the commercial cooling range for cooling the enclosed area therein, often used for transporting foods and other perishable goods. The enclosed area to be cooled may be in the truck or in the trailer portion, and the driving means for the cryogenic engine may be the battery or a separate direct-drive fuel-driven engine mounted on the truck or trailer portion of the vehicle.

Due to the fact that the refrigerant vapors entering the upper portion of the condenser-accumulator do so at a very high linear velocity, it is necessary that the unit contain a multiplicity of condensing surfaces adequate to liquefy the entering refrigerant vapors. These surfaces are desirably mounted in parallel vertical direction, and they should be made of highly heat-conductive material, such as copper, aluminum, or other material which is not adversely affected by the refrigerant liquid employed.

For the reason already stated, it is also highly important that a large amount of vapor flow area be provided within the inner tube to reduce velocity pressure, and because the cooling cycle involves a high vaporliquid ratio. Accordingly, the use of thick wicks and similar capillary flow means which restrict the inner tube area are detrimental.

Comparative refrigeration tests carried out on 1) a system of the present invention employing a 2-cylinder modified Stirling cycle cryogenic engine with a tube array operating on a liquid refrigerant, and (2) a commercial mechanical system employed for refrigerator trucks and also using a refrigerant liquid, gave the results shown in Table I, based on an ambient temperature of F.

TABLE I Refrigeration temperature (Tn) B.t.u./hr. for each kw. input (net usable refrigeration 200 250 260 275 Q,g=lkw. K. K. K. K.

Present invention 1, 500 3, 500 4, 400 6, 300 Commercial system 1, 300 2, 200 2, 800

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more readily understood by reference to the accompanying drawings in which a preferred embodiment is described and in which:

FIG. 1 illustrates a perspective side view of a cryogenic engine, thermal connection, a portion of the tubular array and a condenser-accumulator with thermal connection with the engine of the present invention. A portion of the engine is cut away to reveal the cylinders and pistons, and a portion of the insulation is cut away to disclose the condenser-accumulator and thermal connection.

FIG. 2 depicts an enlarged cross-sectional top view of one type of condenser-accumulator taken along the plane of line 22 in FIG. 3, with covering insulation removed.

FIG. 3 is an enlarged cross-sectional side view of the aforesaid condenser-accumulator taken along the plane of line 3-3 in FIG. 2.

FIG. 4 shows a schematic elevational side view of a truck-trailer equipped with the refrigeration system of the present invention.

FIG. 5 presents a top view of a trailer, such as that shown in FIG. 4.

FIGS. 6-9 depict cross-sectional side views of lengths of tubular arrays suitable for use in the present invention.

FIG. 10 shows a rear view (with rear housing plate removed) of another condenser-accumulator which is abutted against the cold head of the cryogenic engine.

FIG. 11 presents a vertical cross-sectional view, taken along the plane of line 11-11 of FIG. 10.

FIG. 12 illustrates a vertical cross-sectional view of the connection between the condenser-accumulator of FIG. 11 and the tube array.

FIG. 13 depicts a cut-off portion of the outermost end of the tube array, with a portion of the covering insulation cut away.

The same numerals refer to the same or similar parts in the various figures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As already stated, one of the important elements of the present invention is the cryogenic engine, such as a modified Stirling cycle engine indicated generally as 10 and having an electric motor drive in a finned heat-dissipating housing 11. Engine 10 also is provided with a heat-dissipating fin arrangement 12. The motor drives reciprocating compressor piston 13 and expander piston 14. At the ends of the corresponding cylinders 15 and 16, respectively, the cooled fixed gas (helium) passes under cold head 17, made of heat-conductive material, such as copper, silver, or the like. The temperature of this cold head thermal connection may reach l00 F., or even lower.

Mounted on top of cold head 17 is the condenseraccumulator of the tube array, said unit being designated generally as 18. The bottom of this condenser-accumulator 18 is a sheet 19 of heat-conductive material such as copper, or the like. The condenser-accumulator is attached to the cold head by means of clamps, bolts, or the like, and the cold head 17 of the engine must be kept in thermal contact at all times with the thermal connection, such as bottom 19. The unit is covered with insulation 20 to insure against heating up.

The tube array, indicated generally as 21, consists of outer heat-conductive tube 22 and inner concentric tube 23, with space 24 therebetween. One end 25 of array 21 is connected to the side of condenser-accumulator 18, near the bottom thereof, while the rest of the array protrudes into the truck body 39, or other space to be refrigerated. Liquefied refrigerant flows from the bottom of condenser-accumulator 18, by forces due to capillary action, augmented by thermal forces and gravity through annular space 24, and it vaporizes during the cooling process. The vapors return through the inner space 26 of inner tube 23, back to the condenser-accumulator 18 for liquefaction by contact with the condensing surfaces surrounding openings 32 and bottom 19.

As is apparent from FIGS. 2-3, the innermost end 25 of tube array 21 enters the side of condenser-accumulator 18 at opening 27. The inner tube 23 has an extension of solid metal 28 which terminates in a header opening 29 in plate 30, so that the vapors are retained in the upper space 31 of the condenser-accumulator. Metal plate 30 is provided with tapered tubular openings 32 which provide large metal condensing surfaces, and which lead to the bottom portion 33 of the unit, and which serves as a reservoir for the liquefied refrigerant 34. Bottom conductive plate 19 is the thermal connection with 60141 head 17 of engine 10, so that, as refrigerant vapors enter through tube 23 and extension 28, they contact the cold inner surface of the condenser-accumulator and, as they condense, their flow follows a pattern of the arrows shown, so that the condensed liquid passes through tapered tubular openings 32 and is deposited in reservoir 33 for recirculation through annular space 24. A heater 35, having external electrical connections 36, is provided for maintaining a heat balance. Although one row of tubular openings 32 is shown, it is to be understood that any desired number of rows may be employed to insure complete condensation of the vapors.

The inner tube 23 may be made of ordinary heat-conductive tubing (e.g., of copper, aluminum, or the like), as shown in FIG. 1, in which case the vapors, when they reach the end '37 of the outer tube, return through open end 38 of the inner tube, to the condenser-accumulator. Or, as shown in FIG. 6, the inner tube 23 maybe perforated with holes 38 through which the vapors may return. The inner tube 23 may also be made of thin sintered metal 44 which is porous enough to allow vapor passage therethrough. Although circular tubes have been shown, it is possible to employ concentric tubes of other shapes, such as the hexagonal tubes shown in FIG. 8. Also, although tubes of uniform diameter have been shown, it is possible to employ gradually-tapered tubes, such as those depicted in FIG. 9.

When the invention is employed in a tractor trailer, for example, such as trailer 39 in FIG. 4, the system of the present invention is mounted, as shown, with the cryogenic engine and superimposed insulated condenser-accumulator enclosed in an outer housing 40, while the bare concentric tube array 21 is disposed above and within the space in the trailer to be cooled. Such a. tractor may have a series of, say three tube arrays 21, as in 'FIG. 5, all three being connected with header 41 connecting the arrays. Spacers, such as spacers 42 in 'FIG. 6, may be employed to insure concentricity. Also, the outer tubes 22 may be provided with convection and radiation fins, such as fins 43 in FIG. 7.

In 'FIGS. 10-13, there is described a preferred system wherein the inner tube 23 of the array consists of a single layer of woven metal which is inserted into the outer tube 22, leaving an annular space 24 for capillary liquid flow through the annulus. The woven metal tube 23 is desired to be of mesh tight enough to retain the liquid refrigerant on its surface, i.e., support the liquid so it does not drip down through the mesh into the inner vapor space 26. A wire screen of about mesh or higher is suitable for such purpose. Although one layer of this wire mesh is best, it is to be understood that two, or even three, layers may be employed, particularly in the case of large tubes.

The condenser-accumulator 18' has a heavy housing 45 of copper or other heat-conducting material, and is provided with front face 46 and back face 47, which latter is removed in FIG. 10.

As can be seen in FIG. 12, array 21 terminates at its inner end 25 with gasketed union flange 4-9. The bottom outlet 50 of condenser-accumulator 18' also terminates with flange 49', at which point the :bolted u-nion takes place. The inner end 26a is slipped over the outer end 26' of extension 28 (which is a tube of solid (i.e., impermeable) metal), thus making a continuous duct for vapors from the inside of tube 23 to pass through center area 26 and through tube 28 into the condensing area. The junction of tube ends 26a and 26 can be made more secure by means of a serrated or perforated locking ring 51.

Tube 28 is joined to the bottom of hollow triangularshaped spreader chamber 52 in which the vapors expand to the side dimensions of unit 18, and the upper portion of chamber 52 terminates with a forwardly-bent plate 53 which deflects the vapors toward condensing plates 54. These are spaced vertical plates which are attached to forward housing portion 4-6 by conductive supports 55, and the refrigerant vapors pass between these plates downwardly, as they are condensed. The condensate or liquid refrigerant then passes through the annular space 24 between tubes 22 and 23', and is carried, mainly by capillary action, to the end 37 of the array. Meanwhile, the vaporized refrigerant passes through the meshes of tube 23 and enters the inner space 26, through which it travels at high velocity back through tube 28 and to condenser-accumulator 18 for recirculation. The refrigerant liquid flow into the array may be augmented by mechanical pumping means, with liquid being withdrawn from, say an opening 60, and pumped into annulus 24 or 24'.

At the outermost terminus 37 of the array, a heating cable 56, incorporating resistance heating wires 57-5 8 may be wound around the array to increase the local vapor pressure and thus help force the vapor back into the condenseraccumulator 18' in cases where such assistance is required. The cable is covered with insulation 59, and wires 57-58 are connected to a switch and source of electrical power (not shown).

From the aforesaid, it is apparent that the present invention provides a refrigeration system for transport purposes which is compact, convenient and highly efiicient. It is desirable to maintain a low tube thickness, say 0.005" to about 0.25", although thicker tubes may be necessary in the case of excessive lengths and in other special cases. The annulus 24 or 24' between the two concentric tubes of the array will vary, depending upon the viscosity of the refrigerant, and may be about 0.1" to about 0.25" for refrigerants of low viscosity, to about 0.5" or more for viscous refrigerating liquids.

A concentric tube array of 40 ft. length has given an isothermal system with very little maintenance, and it has been possible to guarantee a minimum life of 5,000 hours for the entire system when using helium as the working gas for the cryogenic engine.

I claim: 1

1. A transportable refrigeration system for cooling an enclosed area, comprising:

a transportable vehicle having an enclosed area to be cooled,

a tube array disposed in said area and serving as the area cooler and consisting of at least one combination of two spaced concentric tubes, the outer tube being heat-conductive and closed at one end, said array serving to feed liquid refrigerant, mainly by forces due to capillary action, through the annular space between said tubes, wherein evaporation of said refrigerant effects a cooling, and the space within the inner tube serves to collect separated vapor emitted by said refrigerant during the cooling operation,

an enclosed condenser-accumulator containing a multiplicity of condensing surfaces and having a thermal connection and serving as a condenser and receptacle for said refrigerant and having an opening near its bottom designed to be connected with the outer tube at the other end of said tube array,

an extension on said inner concentric tube of said other end of said array, leading to the upper portion of said condenser-accumulator for venting refrigerant vapor while the condensed refrigerant collected at the bottom thereof may feed into the annular space of said array for recirculation,

a volatile liquid having a boiling point at one atmosphere in the range of about 50 C. to about 50 C. serving as the liquid refrigerant in said array,

a driven two-cylinder modified Stirling cycle cryogenic engine operating on a fixed gas as the working fiuid and disposed on the outside of said area to be cooled and having a cold head in thermal connecting relation with the thermal connection of said condenseraccumulator and serving as the cooling means for said refrigerant vapor, and

driving means disposed on said vehicle for driving said engine.

2. A transportable refrigeration system, according to claim 1, in which the condenser-accumulator contains a multiplicity of parallel vertical metal conductive condensing surfaces between which the refrigerant vapors are passed.

3. A transportable refrigeration system, according to claim 1, in which said condenser-accumulator contains an expansion vessel ahead of said condensing surfaces and to the inlet of which is connected the discharge end of said inner tube extension.

4. A transportable refrigeration system, according to claim 1, in which the inner tube is made of woven wire and of mesh high enough to support said liquid refrigerant on its surface.

5. A transportable refrigeration system, according to claim 4, in which the inner tube extension is made of solid material.

6. A transportable refrigeration system, according to claim 1, in which heating means is attached to the outermost end of said array for increasing the local vapor pressure therein.

7. A process for refrigerating an enclosed area in a transportable vehicle, comprising:

flowing, mainly by capillary action, a liquid refrigerant into an annular space between two concentric heatconductive tubes disposed within said area, during which vaporization of the liquid takes place,

withdrawing the vapors thus formed into and through the inner-tube,

passing the vapors into a condenser-accumulator vessel having a thermal connection with the cold head of a two-cylinder modified Stirling cycle cryogenic engine, and passing said vapors between a multiplicity of condensing surfaces within said vessel, whereby they are condensed to liquid, and

recirculating said liquid, mainly by capillary action,

through said annular space.

8. A process, according to claim 7, in which said refrigerant vapors in said array are passed through a woven metal inner tube of mesh high enough to support the liquid refrigerant, and

withdrawing said vapors through said mesh and through the space inside said inner tube.

9. A process, according to claim 7, in which the vapors entering said condenser-accumulator are expanded before they are passed between said condensing surfaces.

References Cited UNITED STATES PATENTS Levedahl -105 ALBERT W. DAVIS, 111., Primary Examiner U.S. Cl. X.R. 

